In Nevada, may I record audio of my boss making promises to me at work as well as making derogatory statements and comments to me while at work

The answer differs depending on whether the taping is of in-person communications versus telephone conversations.  In Lane v. Allstate Ins. Co., 114 Nev. 1176 (1998), the Nevada Supreme Court compared NRS 200.620 (which restricts taping of telephone calls) with NRS 200.650 (which restricts intrusion into in-person communications). "The legislative intent to prohibit the taping of telephone conversations with the consent of only one party is made clear by comparing the language of NRS 200.620 with the language of NRS 200.650. In NRS 200.650, the legislature prohibited surreptitious intrusion upon in-person, private conversations by means of any listening device, but specifically added the language “'unless authorized to do so by one of the persons engaging in the conversation.'”  Therefore the taping of in-person communications requires only the consent of one of the parties to the conversation, which would presumably be you, pursuant to NRS 200.650.  The taping of telephone conversations requires two-party consent pursuant to NRS 200.620.  "It seems apparent that the legislature believed that intrusion upon Nevadans' privacy by nonconsensual recording of telephone conversations was a greater intrusion than the recording of conversations in person." Id.